Method for forming a low viscosity polyarylene sulfide

ABSTRACT

A method for washing a polyarylene sulfide with a washing solution that contains a carefully controlled solvent content is provided. More particularly, the washing solution typically contains water (e.g., deionized water) in an amount of from about 30 wt. % to about 70 wt. % and an aprotic organic solvent in an amount of from about 30 wt. % to about 70 wt. %. Within such carefully controlled ranges, the present inventors have discovered that the polyarylene sulfide can retain a relatively high oligomer content, which in turn, helps minimize the melt viscosity.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/117,988, filed on Feb. 19, 2015; 62/197,634, filed on Jul.28, 2015; and 62/206,124 filed on Aug. 17, 2015, which are incorporatedherein in their entirety by reference thereto.

BACKGROUND OF THE INVENTION

Polyarylene sulfides are high-performance polymers that may withstandhigh thermal, chemical, and mechanical stresses and are beneficiallyutilized in a wide variety of applications. Polyarylene sulfides aregenerally formed via polymerization of a dihaloaromatic monomer with analkali metal sulfide or an alkali metal hydrosulfide in an organic amidesolvent. Following formation, the polyarylene sulfide is washed toseparate the polymer from the solvent, unreacted monomers, and otherimpurities. Many conventional washing solutions rely on the use ofacetyl compounds (i.e., acetone) to quickly remove the reaction solventand a substantial portion of partially polymerized oligomers from thepolyarylene sulfide. Unfortunately, polyarylene sulfides that are washedwith such acetyl solutions tend to contain residual amounts ofmalodorous compounds, which are generally undesirable. Furthermore, manyalternative organic solvents are problematic in that they tend tosolubilize the oligomers to such a large extent that the melt viscosityof the polymer substantially increases. As such, a need currently existsfor an improved washing technique that does not have a significantadverse impact on the melt viscosity of the resulting polyarylenesulfide.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method forforming a polyarylene sulfide is disclosed. The method comprisescontacting a slurry of a polyarylene sulfide with a washing solution,wherein the washing solution contains from about 30 wt. % to about 70wt. % of water and from about 30 wt. % to about 70 wt. % of an aproticorganic solvent. The polyarylene sulfide has an oligomer content of fromabout 0.5 wt. % to about 2 wt. % and a melt viscosity of about 2,350poise or less, as determined in accordance with ISO Test No. 11443:2005at a shear rate of 1200 s⁻¹ and at a temperature of 310° C.

In accordance with another embodiment of the present invention, a systemfor washing a polyarylene sulfide is disclosed that comprises a slurryof a polyphenylene sulfide, a washing solution that contains from about40 wt. % to about 60 wt. % of water and from about 40 wt. % to about 60wt. % of N-methylpyrrolidone, and a sedimentation column that isconfigured to receive the slurry of the polyarylene sulfide and thewashing solution.

BRIEF DESCRIPTION OF THE FIGURES

The present disclosure may be better understood with reference to thefollowing figures:

FIG. 1 illustrates one embodiment of a sedimentation column that may beemployed in the present invention;

FIG. 2 illustrates a cross-sectional top view of the middle section ofthe sedimentation column of FIG. 1 at the slurry inlet;

FIG. 3 illustrates several different embodiments of longitudinalcross-sectional shapes of a middle section of a sedimentation columnthat may be employed in the present invention; and

FIG. 4 illustrates one embodiment of a washing system that may beemployed in the present invention.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to a method forwashing a polyarylene sulfide with a washing solution that contains acarefully controlled solvent content. More particularly, the washingsolution typically contains water (e.g., deionized water) in an amountof from about 30 wt. % to about 70 wt. %, in some embodiments from about35 wt. % to about 65 wt. %, and in some embodiments, from about 40 wt. %to about 60 wt. %. The washing solution also contains an aprotic organicsolvent in an amount of from about 30 wt. % to about 70 wt. %, in someembodiments from about 35 wt. % to about 65 wt. %, and in someembodiments, from about 40 wt. % to about 60 wt. %. Within suchcarefully controlled ranges, the present inventors have discovered thatthe polyarylene sulfide can retain a relatively high oligomer content,which in turn, helps minimize the melt viscosity. The oligomer contentmay, for instance, range from about 0.5 wt. % to about 2 wt. %, in someembodiments from about 0.8 wt. % to about 1.8 wt. %, and in someembodiments, from about 1.2 wt. % to about 1.6 wt. %. The polyarylenesulfide may likewise have a melt viscosity of about 2,350 poise or less,in some embodiments about 2,300 poise or less, and in some embodiments,from about 1,000 to about 2,280 poise, as determined in accordance withISO Test No. 11443:2005 at a shear rate of 1200 s⁻¹ and at a temperatureof 310° C. In addition, the crystallization temperature of thepolyarylene sulfide may also remain relatively low, such as about 200°C. or less, in some embodiments about 195° C. or less, and in someembodiments, from about 140° C. to about 190° C.

The weight average molecular weight of the polyarylene sulfide may alsobe from about 30,000 to about 60,000 Daltons, in some embodiments about35,000 Daltons to about 55,000 Daltons, and in some embodiments, fromabout 40,000 to about 50,000 Daltons. While having a low molecularweight, the present inventors have surprisingly discovered that thepolydispersity index (weight average molecular weight divided by thenumber average molecular weight) is also relatively low, thus resultingin a polymer that is more readily formed into particles with a narrowparticle size distribution. For instance, the polydispersity index ofthe polyarylene sulfide may be about 4.3 or less, in some embodimentsabout 4.1 or less, and in some embodiments, from about 2.0 to about 4.0.The number average molecular weight of the polyarylene sulfide may, forinstance, be from about 8,000 about 12,500 Daltons, in some embodimentsabout 9,000 Daltons to about 12,500 Daltons, and in some embodiments,from about 10,000 to about 12,000 Daltons.

Various embodiments of the present invention will now be described inmore detail below.

I. Polyarylene Sulfide

The polyarylene sulfide generally has repeating units of the formula:—[(Ar¹)_(n)—X]_(m)—[(Ar²)_(i)—Y]_(j)—[(Ar³)_(k)—Z]_(l)—[(Ar⁴)_(o)—W]_(p)—wherein,Ar¹, Ar², Ar³, and Ar⁴ are independently arylene units of 6 to 18 carbonatoms; W, X, Y, and Z are independently bivalent linking groups selectedfrom —SO₂—, —S—, —SO—, —CO—, —O—, —C(O)O— or alkylene or alkylidenegroups of 1 to 6 carbon atoms, wherein at least one of the linkinggroups is —S—; and n, m, i, j, k, l, o, and p are independently 0, 1, 2,3, or 4, subject to the proviso that their sum total is not less than 2.

The arylene units Ar¹, Ar², Ar³, and Ar⁴ may be selectively substitutedor unsubstituted. Advantageous arylene units are phenylene, biphenylene,naphthylene, anthracene and phenanthrene. The polyarylene sulfidetypically includes more than about 30 mol %, more than about 50 mol %,or more than about 70 mol % arylene sulfide (—S—) units. For example,the polyarylene sulfide may include at least 85 mol % sulfide linkagesattached directly to two aromatic rings. In one particular embodiment,the polyarylene sulfide is a polyphenylene sulfide, defined herein ascontaining the phenylene sulfide structure —(C₆H₄—S)_(n)— (wherein n isan integer of 1 or more) as a component thereof.

The polyarylene sulfide may be a homopolymer or copolymer. For instance,selective combination of dihaloaromatic compounds may result in apolyarylene sulfide copolymer containing not less than two differentunits. For instance, when p-dichlorobenzene is used in combination withm-dichlorobenzene or 4,4′-dichlorodiphenylsulfone, a polyarylene sulfidecopolymer may be formed containing segments having the structure offormula:

and segments having the structure of formula:

or segments having the structure of formula:

The polyarylene sulfide(s) may be linear, semi-linear, branched orcrosslinked. Linear polyarylene sulfides typically contain 80 mol % ormore of the repeating unit —(Ar—S)—. Such linear polymers may alsoinclude a small amount of a branching unit or a cross-linking unit, butthe amount of branching or cross-linking units is typically less thanabout 1 mol % of the total monomer units of the polyarylene sulfide. Alinear polyarylene sulfide polymer may be a random copolymer or a blockcopolymer containing the above-mentioned repeating unit. Semi-linearpolyarylene sulfides may likewise have a cross-linking structure or abranched structure introduced into the polymer a small amount of one ormore monomers having three or more reactive functional groups.

Various techniques may generally be employed to synthesize thepolyarylene sulfide. By way of example, a process for producing apolyarylene sulfide may include reacting a material that provides ahydrosulfide ion (e.g., an alkali metal sulfide) with a dihaloaromaticcompound in an organic amide solvent. The alkali metal sulfide may be,for example, lithium sulfide, sodium sulfide, potassium sulfide,rubidium sulfide, cesium sulfide or a mixture thereof. When the alkalimetal sulfide is a hydrate or an aqueous mixture, the alkali metalsulfide may be processed according to a dehydrating operation in advanceof the polymerization reaction. An alkali metal sulfide may also begenerated in situ. In addition, a small amount of an alkali metalhydroxide may be included in the reaction to remove or react impurities(e.g., to change such impurities to harmless materials) such as analkali metal polysulfide or an alkali metal thiosulfate, which may bepresent in a very small amount with the alkali metal sulfide.

The dihaloaromatic compound may be, without limitation, ano-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalotoluene,dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl, dihalobenzoicacid, dihalodiphenyl ether, dihalodiphenyl sulfone, dihalodiphenylsulfoxide or dihalodiphenyl ketone. Dihaloaromatic compounds may be usedeither singly or in any combination thereof. Specific exemplarydihaloaromatic compounds may include, without limitation,p-dichlorobenzene; m-dichlorobenzene; o-dichlorobenzene;2,5-dichlorotoluene; 1,4-dibromobenzene; 1,4-dichloronaphthalene;1-methoxy-2,5-dichlorobenzene; 4,4′-dichlorobiphenyl;3,5-dichlorobenzoic acid; 4,4′-dichlorodiphenyl ether;4,4′-dichlorodiphenylsulfone; 4,4′-dichlorodiphenylsulfoxide; and4,4′-dichlorodiphenyl ketone. The halogen atom may be fluorine,chlorine, bromine or iodine, and two halogen atoms in the samedihalo-aromatic compound may be the same or different from each other.In one embodiment, o-dichlorobenzene, m-dichlorobenzene,p-dichlorobenzene or a mixture of two or more compounds thereof is usedas the dihalo-aromatic compound. As is known in the art, it is alsopossible to use a monohalo compound (not necessarily an aromaticcompound) in combination with the dihaloaromatic compound in order toform end groups of the polyarylene sulfide or to regulate thepolymerization reaction and/or the molecular weight of the polyarylenesulfide.

Although by no means required, the polyarylene sulfide can, in certainembodiments be formed in a multi-stage process that includes at leasttwo separate formation stages. One stage of the formation process mayinclude reaction of a complex that includes a hydrolysis product of anorganic amide solvent and alkali metal hydrogen sulfide with adihaloaromatic monomer to form a prepolymer. Another stage of theprocess may include further polymerization of the prepolymer to form thefinal product. Optionally, the process may include yet another stage inwhich the organic amide solvent and an alkali metal sulfide are reactedto form the complex. If desired, the different stages may take place indifferent reactors. The utilization of separate reactors for each of thestages may decrease cycle time, as the total cycle time may be equal tothat of the slowest stage, rather than the sum of all stages as in asingle reactor system. In addition, the utilization of separate reactorsmay decrease capital costs, as smaller reactors may be utilized thanwould be necessary for the same size batch in a single reactor system.Moreover, as each reactor need only meet the specifications of the stagebeing carried out in that reactor, a single, large reactor that meetsthe most stringent parameters of all stages of the formation process isno longer necessary, which may further decrease capital costs.

In one embodiment, for instance, a multi-stage process may be employedthat utilizes at least two separate reactors. The first reactor may beutilized for a first stage of the process during which an organic amidesolvent and an alkali metal sulfide react to form a complex thatincludes a hydrolysis product of the organic amide solvent (e.g., analkali metal organic amine carboxylic acid salt) and an alkali metalhydrosulfide. Exemplary organic amide solvents as may be used in aforming the polyarylene sulfide may include, without limitation,N-methyl-2-pyrrolidone; N-ethyl-2-pyrrolidone; N,N-dimethylformamide;N,N-dimethylacetamide; N-methylcaprolactam; tetramethylurea;dimethylimidazolidinone; hexamethyl phosphoric acid triamide andmixtures thereof. The alkali metal sulfide may be, for example, lithiumsulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesiumsulfide or a mixture thereof. An alkali metal sulfide may also begenerated in situ. For instance, a sodium sulfide hydrate may beprepared within the first reactor from sodium hydrogen sulfide andsodium hydroxide that may be fed to the reactor. When a combination ofalkali metal hydrogen sulfide and alkali metal hydroxide are fed to thereactor to form the alkali metal sulfide, the molar ratio of alkalimetal hydroxide to alkali metal hydrogen sulfide may be between about0.80 and about 1.50. In addition, a small amount of an alkali metalhydroxide may be included in the first reactor to remove or reactimpurities (e.g., to change such impurities to harmless materials) suchas an alkali metal polysulfide or an alkali metal thiosulfate, which maybe present in a very small amount with the alkali metal sulfide.

The feed to the first reactor may include sodium sulfide (Na₂S) (whichmay be in the hydrate form), N-methyl-2-pyrrolidone (NMP) and water.Reaction between the water, sodium sulfide and the NMP may form acomplex including sodium methylaminobutyrate (SMAB—a hydrolysis productof NMP) and sodium hydrogen sulfide (NaSH) (SMAB—NaSH) according to thefollowing reaction scheme:

According to one embodiment, a stoichiometric excess of the alkali metalsulfide may be utilized in the first stage reactor, though this is not arequirement of the formation stage. For instance, the molar ratio oforganic amide solvent to sulfur in the feed may be from 2 to about 10,or from about 3 to about 5, and the molar ratio of water to the sulfursource in the feed may be from about 0.5 to about 4, or from about 1.5to about 3.

During the formation of the complex, the pressure within the firstreactor may be held at or near atmospheric pressure. To maintain the lowpressure reaction conditions, vapor may be removed from the reactor. Themain constituents of the vapor may include water and hydrogen sulfideby-product. Hydrogen sulfide of the vapor can, for instance, beseparated at a condenser. A portion of the water that is separated atsuch a condenser may be returned to the reactor to maintain the reactionconditions. Another portion of the water may be removed from the processso as to dehydrate the SMAB—NaSH solution formed in the first stage. Forinstance, the molar ratio of water to NaSH (or the ratio of oxygen tosulfur) in the product solution of the first reactor may less than about1.5, or may be between about 0.1 and about 1 such that the SMAB—NaSHcomplex solution that is fed to the second stage reactor isnear-anhydrous.

Once formed, the SMAB—NaSH complex may then be fed to a second reactorin conjunction with a dihaloaromatic monomer (e.g., p-dichlorobenzene)and a suitable solvent so as to form the polyarylene sulfide prepolymerin the second stage of the process. The amount of the dihaloaromaticmonomer(s) per mole of the effective amount of the charged alkali metalsulfide may generally be from about 1.0 to about 2.0 moles, in someembodiments from about 1.05 to about 2.0 moles, and in some embodiments,from about 1.1 to about 1.7 moles. If desired, the dihaloaromaticmonomer may be charged into the second reactor with a relatively lowmolar ratio of the dihaloaromatic monomer to the alkali metal hydrogensulfide of the complex. For instance, the ratio of the dihaloaromaticmonomer to sulfur charged to the second reactor may be from about 0.8 toabout 1.5, and in some embodiments, from about 1.0 to about 1.2. Therelatively low ratio of the dihaloaromatic monomer to the alkali metalhydrogen sulfide of the complex may be favorable for the formation ofthe final high molecular weight polymer via the condensationpolymerization reaction. The ratio of solvent to sulfur in the secondstage may also be relatively low. For instance, the ratio of the alkalimetal hydrogen sulfide of the complex to the organic amide solvent inthe second stage (including the solvent added to the second reactor andsolvent remaining in the complex solution from the first reactor) may befrom about 2 to about 2.5. This relatively low ratio may increase theconcentration of reactants in the second reactor, which may increase therelative polymerization rate and the per volume polymer production rate.

The second reactor may include a vapor outlet for removal of vaporduring the second stage in order to maintain the desired pressure level.For instance, the second reactor may include a pressure relief valve asis known in the art. Vapor removed from the second stage may becondensed and separated to recover unreacted monomer for return to thereactor. A portion of the water of the vapor may be removed to maintainthe near-anhydrous conditions of the second stage, and a portion of thewater may be returned to the second reactor. A small amount of water inthe second reactor may generate reflux in the top of the reactor, whichmay improve separation between the water phase and the organic solventphase in the reactor. This may in turn minimize loss of the organicsolvent in the vapor phase removed from the reactor as well as minimizeloss of hydrogen sulfide in the vapor stream due to absorption of thehydrogen sulfide by the highly alkaline organic solvent as discussedpreviously.

The second stage polymerization reaction may generally be carried out ata temperature of from about 200° C. to about 280° C., or from about 235°C. to about 260° C. The duration of the second stage may be, e.g., fromabout 0.5 to about 15 hours, or from about 1 to about 5 hours. Followingthe second stage polymerization reaction, the mean molar mass of theprepolymer as expressed by the weight average molecular weight, M_(w),may be from about 500 g/mol to about 30,000 g/mol, from about 1000 g/molto about 20,000 g/mol, or from about 2000 g/mol to about 15,000 g/mol.

Following the second stage polymerization reaction, the product solutionthat exits second stage reactor may include the prepolymer, the solvent,and one or more salts that are formed as a by-product of thepolymerization reaction. For example, the proportion by volume of theprepolymer solution exiting the second stage reactor of salt that isformed as a byproduct to the reaction may be from about 0.05 to about0.25, or from about 0.1 to about 0.2. Salts included in the reactionmixture may include those formed as a byproduct during the reaction aswell as other salts added to the reaction mixture, for instance as areaction promoter. The salts may be organic or inorganic, i.e., mayconsist of any combination of organic or inorganic cations with organicor inorganic anions. They may be at least partially insoluble in thereaction medium and have a density different from that of the liquidreaction mixture. According to one embodiment, at least a portion of thesalts in the prepolymer mixture that exits the second stage reactor maybe removed from the mixture. For instance, the salts may be removed byuse of screens or sieves as has been utilized in traditional separationprocesses. A salt/liquid extraction process may alternatively oradditionally be utilized in separating the salt from the prepolymersolution. In one embodiment, a hot filtration process may be utilized inwhich the solution may be filtered at a temperature at which theprepolymer is in solution and the salts are in the solid phase.According to one embodiment, a salt separation process may remove about95% or more of the salts including in the prepolymer solution that exitsthe second reactor. For instance greater than about 99% of the salts maybe removed from the prepolymer solution.

Following the prepolymer polymerization reaction in the second stage ofthe process and the filtration process, an optional third stage of theformation may take place during which the molecular weight of theprepolymer is increased in a third reactor. Input to the third reactormay include the prepolymer solution from the second reactor in additionto solvent, one or more dihaloaromatic monomers, and a sulfur-containingmonomer. For instance, the amount of the sulfur-containing monomer addedin third stage may be about 10% or less of the total amount required toform the product polyarylene sulfide. In the illustrated embodiment, thesulfur-containing monomer is sodium sulfide, but this is not arequirement of the third stage, and other sulfur containing monomers,such as an alkali metal hydrogen sulfide monomer may alternatively beutilized.

The third reaction conditions may be nearly anhydrous, with the ratio ofwater to the sulfur-containing monomer less than about 0.2, for instancebetween 0 and about 0.2. The low water content during the third stage ofthe process may increase the polymerization rate and the polymer yieldas well as reduce formation of undesired side reaction by-products asthe conditions are favorable for nucleophilic aromatic substitution, asdiscussed above. Moreover, as pressure increases in the third stage aregenerally due to water vaporization, low water content during this stagemay allow the third reaction to be carried out at a constant, relativelylow pressure, for instance less than about 1500 kPa. As such, the thirdreactor 104 need not be a high pressure reactor, which may providesubstantial cost savings to a formation process as well as decreasesafety risks inherent to high pressure reactors.

The reaction conditions within the third reactor may also include arelatively low molar ratio for the solvent to the sulfur-containingmonomer. For instance, the ratio of solvent to sulfur-containing monomermay be from about 2 to about 4, or from about 2.5 to about 3. Thereaction mixture of the third stage may be heated to a temperature offrom about 120° C. to about 280° C., or from about 200° C. to about 260°C. and the polymerization may continue until the melt viscosity of thethus formed polymer is raised to the desired final level. The durationof the second polymerization step may be, e.g., from about 0.5 to about20 hours, or from about 1 to about 10 hours. The weight averagemolecular weight of the formed polyarylene sulfide may vary as is known,but in one embodiment may be from about 1000 g/mol to about 500,000g/mol, from about 2,000 g/mol to about 300,000 g/mol, or from about3,000 g/mol to about 100,000 g/mol.

Following the third stage, and any desired post-formation processing,the polyarylene sulfide may be discharged from the third reactor,typically through an extrusion orifice fitted with a die of desiredconfiguration, cooled, and collected. Commonly, the polyarylene sulfidemay be discharged through a perforated die to form strands that aretaken up in a water bath, pelletized and dried. The polyarylene sulfidemay also be in the form of a strand, granule, or powder.

II. Washing Technique

Regardless of the particular manner in which the polyarylene sulfide isformed, it is contacted with a washing solution containing carefullycontrolled amounts of water and an aprotic organic solvent, as notedabove. Particularly suitable aprotic organic solvents include, forinstance, halogen-containing solvents (e.g., methylene chloride,1-chlorobutane, chlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane,chloroform, and 1,1,2,2-tetrachloroethane); ether solvents (e.g.,diethyl ether, tetrahydrofuran, and 1,4-dioxane); ketone solvents (e.g.,acetone and cyclohexanone); ester solvents (e.g., ethyl acetate);lactone solvents (e.g., butyrolactone); carbonate solvents (e.g.,ethylene carbonate and propylene carbonate); amine solvents (e.g.,triethylamine and pyridine); nitrile solvents (e.g., acetonitrile andsuccinonitrile); amide solvents (e.g., N,N′-dimethylformamide,N,N′-dimethylacetamide, tetramethylurea and N-methylpyrrolidone);nitro-containing solvents (e.g., nitromethane and nitrobenzene); sulfidesolvents (e.g., dimethylsulfoxide and sulfolane); and so forth.Regardless of the particular solvents employed, the entire solventsystem (e.g., water and N-methylpyrrolidone) typically constitutes fromabout 80 wt. % to 100 wt. %, in some embodiments from about 85 wt. % to100 wt. %, and in some embodiments, from about 90 wt. % to 100 wt. % ofthe washing solution.

Of course, various other suitable materials may also be used in thewashing solution, such as stabilizers, surfactants, pH modifiers, etc.For example, basic pH modifiers may be employed to help raise the pH ofthe washing solution to the desired level, which is typically above 7,in some embodiments from about 8.0 to about 13.5, in some embodimentsfrom about 9.0 to about 13.5, and in some embodiments, from about 11.0to about 13.0. Suitable basic pH modifiers may include, for instance,ammonia, alkali metal hydroxides (e.g., sodium hydroxide, lithiumhydroxide, potassium hydroxide, etc.), alkaline earth metal hydroxides,etc., as well as combinations thereof. Nevertheless, one beneficialaspect of the present invention is that good properties may be providedwithout the need for various types of conventional additives. Forexample, the washing solution may be generally free of acetyl compounds(e.g., acetone and/or acetic acid), which are conventionally required toachieve a polyarylene sulfide having a high degree of purity. Thewashing solution may thus contain acetyl compounds (e.g., acetone and/oracetic acid) in an amount of no more than about 0.1 wt. %, in someembodiments no more than about 0.05 wt. %, and in some embodiments, andin some embodiments, no more than about 0.01 wt. % of the washingsolution. Of course, in certain embodiments, higher amounts of acetonemay be employed in the washing solution if so desired.

The temperature of the washing solution can also be controlled to helpfacilitate the washing process. For instance, the temperature of thesolution may be from about 10° C. to about 150° C., in some embodimentsfrom about 15° C. to about 120° C., in some embodiments from about 20°C. to about 100° C., and in some embodiments, from about 15° C. to about40° C. In certain cases, heating may be conducted at a temperature thatis above the atmospheric pressure boiling point of a solvent in themixture. In such embodiments, the heating is typically conducted under arelatively high pressure, such as above 1 atm, in some embodiments aboveabout 2 atm, and in some embodiments, from about 3 to about 10 atm.

The manner in which the polyarylene sulfide is contacted with thewashing solution may vary as desired. In one embodiment, for instance, asystem may be employed in which the polyarylene sulfide is contactedwith the washing solution within a vessel, such as a bath, sedimentationcolumn, etc. Referring to FIGS. 1-3, for instance, one embodiment of asedimentation column 10 is shown that is configured to receive apolyarylene sulfide and washing solution. The sedimentation column 10may include an upper section 12 that includes liquid outlet 20, a middlesection 14 that includes inlet 24, and a lower section 16 that includesa solids outlet 22 and a liquid inlet 26. Though illustrated with avertical arrangement, it should be understood that the sedimentationcolumn may be utilized at other than a vertical arrangement, and thesedimentation column may be at an angle to vertical as long as solidsflow through the sedimentation column from the inlet 24 to the outlet 22may be by gravitational force.

The upper section 12 and the lower section 16 may have cross sectionalareas that are larger than that of the middle section 14. In oneembodiment, the sections of the sedimentation column 10 may be circularin cross section, in which case the upper section 12 and lower section16 may have cross sectional diameters that are larger than the crosssectional diameter of the middle section 14. For instance, the uppersection 12 and the lower section 16 may have diameters that are fromabout 1.4 to about 3 times greater than the diameter of the middlesection. For instance, the upper and lower sections may independentlyhave diameters that are about 1.4, about 2, or about 2.5 times greaterthan the diameter of the middle section 14. The larger cross sectionalarea of the upper section 12 may prevent overflow of solids at theoutlet 20 and the larger cross sectional area of the lower section 16may prevent solids flow restriction at the outlet 22. It should beunderstood that the sedimentation column 10 is not limited to anyparticular geometric shape and the cross section of the sedimentationcolumn is not limited to circular. Moreover, the cross sectional shapeof each section of the sedimentation column may vary with regard to oneanother. For example, one or two of the upper section 12, the middlesection 14, and the lower section 16 may have an oval-shaped crosssection, while the other section(s) may be round in cross section.

The middle section 14 of the sedimentation column 10 may include aninlet 24 through which a polymer slurry may be fed to the sedimentationcolumn 10. The slurry may include the polyarylene sulfide in conjunctionwith other byproducts from the formation process, such as reactionsolvents (e.g., N-methylpyrrolidone), salt byproducts, unreactedmonomers or oligomers, etc. As shown in FIG. 2, the inlet 24 meets awall 25 of the middle section 14 substantially tangent to the wall 25.The term “substantially tangent” as utilized herein may be determined bythe distance between the true tangent of the wall 25 of the middlesection 14 and the outer wall 27 of the inlet 24. When the inlet 24meets the wall 25 of the middle section at a perfect tangent, thisdistance will be 0. In general, this distance will be less than about 5centimeters, for instance less than about 3 centimeters. Placement ofthe inlet 24 such that the inlet 24 is substantially tangent to theouter wall 25 of the middle section 14 may prevent disruption of thefluid flow pattern within the sedimentation column 10. This may improvecontact and mass transfer between the downward flowing solids and theupward flowing liquid and may also prevent loss of solids through theoutlet 20 of the upper section 12. To further ensure that solids are notlost through the outlet 20, the inlet 24 may be placed in the middlesection 14 at a distance from the junction 23 where the middle section14 meets the upper section 12. For instance, the vertical distancebetween the midpoint of the inlet 24 and the junction 23 may be equal toor greater than about 5% of the total height of the middle section 14.For instance, the vertical distance between the midpoint of the inlet 24and the junction 23 may be from about 5% to about 50% of the totalheight of the middle section 14. The total height of the middle section14 is that distance between the junction 23, where the upper section 12meets the middle section 14 and the junction 21, where the middlesection 14 meets the lower section 16.

The line at inlet 24 may carry the slurry from a polymerization reactionapparatus to the middle section 14 of the sedimentation column 10. Themiddle section 14 of the sedimentation column may include an agitator 30that incorporates an axial shaft 31 and a series of stirring blades 32along the axial length of the middle section 14. The agitator 30 mayminimize channeling of liquid within the sediment (fluidized bed) andmay maintain contact between the slurry contents and the upwardlyflowing solvent as well as maintain flow of the solids through thesedimentation column 10. The stirring blades 32 may extend from theaxial shaft 31 toward the wall 25 of the middle section 14. In general,the stirring blades may extend at least half of the distance from theaxial shaft to the wall 25 and, in one embodiment, may extend almost allof the way to the wall 25. In one embodiment, the sedimentation columnmay be free of sedimentation plates or trays as have been utilized inpreviously known sedimentation columns.

As shown, the axial shaft 31 may support a series of stirring blades 32along the length of the middle section 14. In general, at least twostirring blades 32 may extend from the axial shaft 31 in a balancedarrangement at each point of blade extension. This is not a requirement,however, and three, four, or more stirring blades may extend from theaxial shaft 31 at a single location along the shaft 31 or alternatively,a single blade may extend from a single location on the shaft 31 and thestirring blades may be offset from one another as they pass down thelength of the shaft 31 so as to maintain balance of the agitator 30during use. The axial shaft 31 may have stirring blades 32 extendingtherefrom at a plurality of locations along the shaft 31. For instance,the axial shaft may have stirring blades extending therefrom at fromabout 3 to about 50 locations along axial shaft 31, with two or morestirring blades 32 extending from the axial shaft at each location. Inone embodiment, the distribution of the blades along the axial shaft 31may be such that there are more blades in the fluidized bed section atthe bottom as compared to the number of blades in the upper portion ofsection 14. During operation, the axial shaft 31 may rotate at a speedthat is typically from about 0.1 rpm to about 1000 rpm, for instancefrom about 0.5 rpm to about 200 rpm or from about 1 rpm to about 50 rpm.

In the illustrated embodiment, a countercurrent flow is employed inwhich the polymer slurry flow is in a direction opposite to that of theflow of the washing solution. Referring again to FIG. 1, for instance,the polymer slurry is fed to the middle section 14 of the sedimentationcolumn 10 via the inlet 24. The washing solution is, on the other hand,fed to the lower section 16 of the column 10 via an inlet 26. In thismanner, the washing solution can flow upwardly through the column as itcontacts the polymer slurry as it flows downwardly through the columntowards the solids outlet 22. If desired, the inlet 26 may include adistributor 35 that may enhance fluid flow through the solids andprevent solids from entering the inlet 26. The lower section 16 may alsohave a conical shape to concentrate the solids content at the outlet 22.The solids content of the slurry at the outlet 22 may generally be about20 wt. % or greater, or about 22 wt. % or greater in some embodiments.If desired, the washing solution may be heated prior to being fed to theinlet 26, such as described above. In such embodiments, thesedimentation column may include heating elements to maintain anelevated temperature during the washing process.

If desired, a fluidized bed may also be formed in the sedimentationcolumn with increasing concentration of solids from the top of the bedto the solids outlet 22. The fluidized bed height may be monitored andcontrolled so as to better control the residence time of solids in thesedimentation column. Through improved control of residence time for thesedimentation column, the efficiency of the separation process carriedout within the sedimentation column may be improved, which may translateto lower operational costs and improved separations. In addition,control of the fluidized bed height and residence time may help toprevent solids loss through the liquid outlet 20 of the upper section12. A sensor may be used to monitor the fluidized bed height within thesedimentation column 10. The sensor type is not limited and may be anysuitable sensor that may monitor the fluidized bed height including bothinternal sensors and external sensors. For example, sensors may utilize,without limitation, optical, infrared, radio frequency, displacement,radar, bubble, vibrational, acoustic, thermal, pressure, nuclear and/ormagnetic detection mechanisms to determine the fluidized bed heightwithin the sedimentation column 10. By way of example, in oneembodiment, an optical sensor 40 (e.g., a laser-based sensor including alaser source and a detector) may be located within the middle section 14of the sedimentation column 10, for instance near the level of the inlet24, which may detect reflection of the laser to determine relativedensity differences of the materials within the sedimentation column 10and thus convey information concerning the location of the top of thefluidized bed to a control system. The control system may relay thatinformation to a valve that may control flow of solids out of thesedimentation column at outlet 22 and/or a valve that may control flowof solids into the sedimentation column at inlet 24 so as to control thebed height. Surge tanks may also be included in the lines leading to andfrom the sedimentation column as is known to maintain control of thefluidized bed height. Other systems as are known in the art forcontrolling the height of a fluidized bed may alternatively be utilized,and the method and system utilized to control the bed height is notparticularly limited. The top of the fluidized bed may be at or near theinlet 24. To improve control of the residence time of the solids in thesedimentation column 10, the sediment bed height variation during theprocess may vary less than about 10% of the total height of the middlesection 14. For instance, the fluidized bed height variation during aprocess may be less than about 5% of the total height of the middlesection 14.

Though illustrated in FIG. 1 as a cylindrical column, the longitudinalcross-sectional shape of the middle section 14 is not limited to thisembodiment. For example, and as illustrated in FIG. 3, middle sections14 a, 14 b, and 14 c of sedimentation columns may be straight or taperedwith increasing angles from a cylindrical middle section as illustratedat 14 a to increasing angles as shown at 14 b and 14 c. When tapered,the middle section may be wider at the top than at the bottom so as toincrease solids concentration at the bottom of the sedimentation columnwithout impeding transport of solids. That is, if the angle of taper istoo large, solids flow may be impeded at the wall of the middle section.A preferred taper angle will vary for each system depending upon flowrates, physical properties of the compounds to be carried within thesystem such as particle size and shape, as well as depending on columnmaterials and surface roughness.

In certain embodiments, the polyarylene sulfide can be contacted withthe washing solution of the present invention in a single step. Forexample, a single sedimentation column can be employed within which thepolyarylene sulfide is washed. In alternative embodiments, however,multiple washing steps may be employed. The washing solutions employedin the stages of such a process need not be the same, and the washingsolution of the present invention can be employed in one stage or inmultiple stages. In one embodiment, for instance, multiple sedimentationcolumns may be used in series, one or more of which have acountercurrent flow such as described above.

Referring to FIG. 4, for instance, one embodiment of a washing processis shown that employs three sedimentation columns 101 a, 101 b, and 101c in series. While the system may include one or more sedimentationcolumns having the design as described above, this is not a requirementof the disclosed systems. For instance, the system may includesedimentation columns that vary somewhat in design from thesedimentation column described above, e.g., the sedimentation columns ofthe system of FIG. 4 do not include upper and lower sections having alarger cross sectional area as compared to the middle section. In anycase, the system may include multiple sedimentation columns 101 a, 101b, and 101 c in series.

To initiate flow through the first sedimentation column 101 a, it may beinitially supplied with a polymer slurry via inlet 124 a. A firstwashing solution 302 may likewise be supplied to the column 101 viainlet 126 a. The first washing solution 302 will generally flow upwardlythrough the column in a direction counter to that of the polymer slurryuntil reaching an outlet 120 a, where a first wash product 402 isremoved which may include the solution and dissolved compounds of thepolymer slurry feed. As shown, a solids outlet 122 a may thereafter feedsolids from the first sedimentation column 101 a to a slurry inlet 124 bof the second sedimentation column 101 b. A second washing solution 304will generally flow upwardly through the column 101 b via an inlet 126 bin a direction counter to that of the solids until reaching an outlet120 b, where a second wash product 404 is removed. Although notrequired, the second washing solution 304 can be a recycle stream thatis removed from the third sedimentation column 101 c via an outlet 120c. In the final sedimentation column 101 c, the solids from the secondsedimentation column may be fed via inlet 124 c. A third washingsolution 306 will generally flow upwardly through the column 101 c viaan inlet 126 c in a direction counter to that of the solids, which exitsthe column via an outlet 122 c to form the polymer product 406.

As noted above, the washing solutions employed in each stage of thewashing process may vary, if desired. For instance, the first washingsolution 302 may be formed from water and an aprotic organic solvent(e.g., N-methylpyrrolidone) in accordance with the present invention.The second washing solution 304 and/or the third washing solution 306may be formed from a similar solution or from a solution that containsonly water or only an organic solvent (e.g., N-methylpyrrolidone).Regardless, once washed the resulting polyarylene sulfide may be driedaccording to any technique known in the art. Drying may occur at atemperature of from about 80° C. to about 250° C., in some embodimentsfrom about 100° C. to about 200° C., and in some embodiments, from about120° C. to about 180° C. The purity of the resulting polyarylene sulfidemay be relatively high, such as about 95% or more, or about 98% or more.

Test Methods

Molecular Weight:

A sample of PPS may be initially converted to PPSO by oxidation with amixture of cold HNO₃ (50%) in a trifluoroacetic acid mixture. Theresulting PPSO may be dissolved in warm hexafluoroisopropanol (HFIP) for1 hour and then analyzed for molecular weight by GPC equipped withPSS-hexafluoroisopropanol (HFIP) gel columns. The gel columns may befitted with an HFIP-gel guard column using HFIP as mobile phase andrefractive index (RI) as detector.

Melt Viscosity:

The melt viscosity may be determined as scanning shear rate viscosityand determined in accordance with ISO Test No. 11443:2005 (technicallyequivalent to ASTM D3835-08) at a shear rate of 1200 s⁻¹ and at atemperature of about 310° C. using a Dynisco 7001 capillary rheometer.The rheometer orifice (die) may have a diameter of 1 mm, a length of 20mm, an L/D ratio of 20.1, and an entrance angle of 180°. The diameter ofthe barrel may be 9.55 mm+0.005 mm and the length of the rod was 233.4mm. Prior to measurement, samples are dried in a vacuum oven for 1.5hours at 150° C.

Crystallization Temperature:

The crystallization temperature may be determined by differentialscanning calorimetry (“DSC”) as is known in the art. Under the DSCprocedure, samples are heated during a first heating cycle at a rate of50° C. per minute to a temperature of 340° C., cooled at a rate of 10°C. per minute to a temperature of 50° C., and then heated during asecond heating cycle at a rate of 50° C. per minute to a temperature of340° C., and cooled again at a rate of 10° C. per minute to atemperature of 50° C. using DSC measurements conducted on a TA Q2000Instrument. The temperature at the highest point of the exothermic curveobtained during the second heating cycle is generally referred to hereinas the “crystallization temperature.”

Oligomer Content:

The oligomer content of a sample may be determined by contacting thesample with an extraction solution that contains 100 wt. % chloroform ata temperature of 60° C. and pressure of 1,500 psi. The sample is rinsedtwice with the extraction solution, and thereafter the extracted solventis dried and the weight of the extractables is measured. The oligomercontent is determined by dividing the weight of the extractables by theweight of the original sample, and then multiplying by 100.

pH:

The resin pH is measured in a mixed solvent of water/acetone (volumeratio=2/1). Liquid pH is measured by initially filtering solids from thewashing liquid, and thereafter measuring pH with a standard pH meter.

EXAMPLE

Eleven (11) samples of a PPS slurry are initially filtered to remove theliquid portion. The resulting PPS flakes are manually charged into areactor vessel and then stirred with the appropriate solvent wash for aset time. The process includes the use of two (2) or three (3) initialwashes with an organic solvent (e.g., acetone, NMP, or a NMP:watermixture), followed by five (5), seven (7), or eleven (11) washes with100% water. For Samples 10-11, the pH in the last water wash step isadjusted to at least 12.0 by the addition of 5% NaOH solution to thewater. The total washing time is 20 minutes, and the drain time is 12minutes for the organic solvent wash steps and 6 minutes for the waterwash steps. Once drained, the bottom drain and filter are removed andthe solids are collected in a pan and dried under vacuum of about 15psig for 16 hours at a temperature of 105° C. A small purge of air ismaintained in the oven to minimize condensation of NMP on the walls. Thewashing conditions are summarized below.

pH of the # of Wash Last Wt. Ratio of Organic # of Water Temp, WashingSample Organic Solvent Solvent/PPS Washes Washes ° C. Liquid 1 100%Acetone 5.5 2 5 20 — 2 100% Acetone 3.5 2 5 20 — 3 100% NMP 3.5 2 5 20 —4  50% NMP: 50% H2O 5.5 2 5 20 — 5  75% NMP: 25% H2O 3.5 2 5 20 9.64 6 75% NMP: 25% H2O 3.5 2 5 20 9.64 7  75% NMP: 25% H2O 3.5 2 7 20 9.28 8 75% NMP: 25% H2O 3.5 2 7 20 9.28 9  75% NMP: 25% H2O 5.5 3 11 74 8.2310  75% NMP: 25% H2O 3.5 2 7 24 12.02 11  75% NMP: 25% H2O 5.5 3 11 7412.17

The resulting polymer samples are then tested as described above. Theresults are set forth below.

Melt Viscosity Crystallization % Sample at 1200 s⁻¹ Temperature, ° C.Resin pH Oligomers 1 2,254 190.4 9.9 1.21 2 2,285 193.8 10.0 1.28 32,314 193.2 10.2 0.58 4 2,032 202.7 10.0 1.48 5 1,990 193.4 10.1 1.43 62,094 191.7 10.1 1.43 7 1,936 192.3 10.1 1.41 8 2,004 198.0 9.9 1.59 91,715 224.3 7.4 1.38 10 2,128 210.7 11.0 1.46 11 2,532 192.8 11.3 1.34

While particular embodiments of the present disclosure have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications may be made withoutdeparting from the spirit and scope of the disclosure. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this disclosure.

What is claimed is:
 1. A method for forming a washed polyarylenesulfide, the method comprising contacting a slurry of a polyarylenesulfide with a washing solution within a vessel in which the slurry ofthe polyarylene sulfide enters the vessel at a slurry inlet that islocated such that solids of the slurry flow via a gravity flow from theslurry inlet to a solids outlet and in which the washing solution entersthe vessel at a liquid inlet and flows counter current to the gravityflow of the solids to a liquid outlet that is above the slurry inlet,wherein the washing solution contains from about 30 wt. % to about 70 wt% of water and from about 30 wt. % to about 70 wt. % of an aproticorganic solvent, wherein the washed polyarylene sulfide has an oligomercontent of from about 0.5 wt. % to about 2 wt. % and a melt viscosity ofabout 2,350 poise or less, as determined in accordance with ISO Test No.11443:2005 at a shear rate of 1200 s⁻¹ and at a temperature of 310° C.2. The method of claim 1, wherein the aprotic organic solvent isN-methylpyrrolidone.
 3. The method of claim 1, wherein the washingsolution has a pH level of from about 8.0 to about 13.5.
 4. The methodof claim 1, wherein the washing solution is generally free of acetone.5. The method of claim 1, wherein the washing solution is at atemperature of from about 15° C. to about 120° C.
 6. The method of claim1, wherein the slurry of the polyarylene sulfide is contacted with thewashing solution within a sedimentation column.
 7. The method of claim1, wherein the washed polyarylene sulfide has an oligomer content offrom about 1.2 wt. % to about 1.6 wt. %.
 8. The method of claim 1,wherein the washed polyarylene sulfide has a melt viscosity of fromabout 1,000 to about 2,280 poise, as determined in accordance with ISOTest No. 11443:2005 at a shear rate of 1200 s⁻¹ and at a temperature of310° C.
 9. The method of claim 1, wherein the washed polyarylene sulfidehas a crystallization temperature of about 200° C. or less.
 10. Themethod of claim 1, wherein the washed polyarylene sulfide has apolydispersity index of about 4.3 or less.
 11. The method of claim 10,wherein the washed polyarylene sulfide has a weight average molecularweight of from about 30,000 to about 60,000 Daltons.
 12. The method ofclaim 10 wherein the washed polyarylene sulfide has a number averagemolecular weight of from about 8,000 about 12,500 Daltons.
 13. Themethod of claim 1, wherein the washed polyarylene sulfide is a linearpolyphenylene sulfide.
 14. The method of claim 1, further comprisingcontacting the washed polyarylene sulfide with an additional washingsolution.
 15. The method of claim 14, wherein the additional washingsolution contains water.
 16. The method of claim 1, further comprisingdrying the washed polyarylene sulfide after contact with the washingsolution.
 17. The method of claim 14, wherein the washed polyarylenesulfide is further contacted with the additional washing solution in asecond vessel in which the washed polyarylene sulfide flows via gravityflow counter current to the additional washing solution.
 18. The methodof claim 17, wherein the additional washing solution is fed to thesecond vessel from a third vessel, the washed polyarylene sulfide beingfurther contacted with the additional washing solution in the thirdvessel.